@article {wu_plate_2023,
	title = {Plate Age and Uppermost Mantle Structure Across the Juan de Fuca and Gorda Plates},
	journal = {Journal of Geophysical Research: Solid Earth},
	volume = {128},
	number = {8},
	year = {2023},
	note = {_eprint: https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2023JB026494},
	pages = {e2023JB026494},
	abstract = {To test the relationship between plate age and uppermost mantle structure for the Juan de Fuca and Gorda plates, as well as the mode of lithospheric cooling, we produce a new 3D oceanic shear wave speed (VS) model. This model is constructed using a new high-quality Rayleigh wave phase speed data set across the plates and is based on a novel thermo-seismic hybrid parameterization. In the lithosphere, we find that the VS structure is primarily (68\% of study area) governed by conductive cooling. Exceptions are observed, suggesting advective heat influx along ridges and hydrothermal circulation through cracks near the subduction trench and transform faults. In the asthenosphere of the Juan de Fuca plate, no simple monotonic relationship between seismic structure and plate age exists, but instead there is a non-monotonic slow-fast-slow VS pattern from west to east. The two slow asthenospheric VS anomalies indicate the presence of partial melt beneath both the mid-ocean ridge and the subduction trench. The partial melt beneath the trench is enigmatic.},
	keywords = {asthenosphere, Juan de Fuca, Lithosphere, plate age, thermal structure, Vs model},
	issn = {2169-9356},
	doi = {10.1029/2023JB026494},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2023JB026494},
	author = {Wu, Mengyu and Wang, Hongda and Zhang, Shane and Ritzwoller, Michael H.}
}
@article {eilon_sub-lithospheric_2022,
	title = {Sub-Lithospheric Small-Scale Convection Tomographically Imaged Beneath the Pacific Plate},
	journal = {Geophysical Research Letters},
	volume = {49},
	number = {18},
	year = {2022},
	note = {_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1029/2022GL100351},
	month = {09/2022},
	pages = {e2022GL100351},
	abstract = {Small-scale convection beneath the oceanic plates has been invoked to explain off-axis nonplume volcanism, departure from simple seafloor depth-age relationships, and intraplate gravity lineations. We deployed 30 broadband ocean bottom seismometer stations on \~{}40 Ma Pacific seafloor in a region notable for gravity anomalies, measured by satellite altimetry, elongated parallel to plate motion. P-wave teleseismic tomography reveals alternating upper mantle velocity anomalies on the order of {\textpm}2\%, aligned with the gravity lineations. These features, which correspond to \~{}300{\textdegree}{\textendash}500{\textdegree}K lateral temperature contrast, and possible hydrous or carbonatitic partial melt, are{\textemdash}surprisingly{\textemdash}strongest between 150 and 260 km depth, indicating rapid vertical motions through a low-viscosity asthenospheric channel. Coherence and admittance analysis of gravity and topography using new multibeam bathymetry soundings substantiates the presence of mantle density variations, and forward modeling predicts gravity anomalies that qualitatively match observed lineations. This study provides observational support for small-scale convective rolls beneath the oceanic plates.},
	keywords = {asthenosphere, body wave tomography, mantle convection, ocean bottom seismometer, oceanic lithosphere},
	issn = {1944-8007},
	doi = {10.1029/2022GL100351},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2022GL100351},
	author = {Eilon, Zachary C. and Zhang, Lun and Gaherty, James B. and Forsyth, Donald W. and Russell, Joshua B.}
}
@article {saikia_upper_2021,
	title = {Upper Mantle Anisotropic Shear Velocity Structure at the Equatorial Mid-Atlantic Ridge Constrained by Rayleigh Wave Group Velocity Analysis From the PI-LAB Experiment},
	journal = {Geochemistry, Geophysics, Geosystems},
	volume = {22},
	number = {3},
	year = {2021},
	note = {_eprint: https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2020GC009495},
	month = {02/2021},
	pages = {e2020GC009495},
	abstract = {The evolution of ocean lithosphere and asthenosphere are fundamental to plate tectonics, yet high resolution imaging is rare. We present shear wave velocity and azimuthal anisotropy models for the upper mantle from Rayleigh wave group velocities from local earthquake and ambient noise at 15{\textendash}40-s period recorded by the Passive Imaging of the Lithosphere Asthenosphere Boundary experiment at the equatorial Mid-Atlantic Ridge covering 0{\textendash}80-Myr-old seafloor. We find slow velocities along the ridge, with faster velocities beneath older seafloor. We image a fast lid (25{\textendash}30-km thick) beneath the ridge that increases to 50{\textendash}60 km beneath older seafloor. Punctuated, \~{}100 km wide low velocity anomalies exist off-axis. There are multiple layers of azimuthal anisotropy, including (i) a lithosphere (20{\textendash}40 km depth) characterized by strong anisotropy (4.0\%{\textendash}7.0 \%) with fast-axes that rotate from ridge subparallel toward the absolute plate motion/spreading direction at distances >60 km from the ridge, and (ii) weak anisotropy (1.0\%{\textendash}2.0\%) at >40 km depth. Our results are consistent with conductive cooling of lithosphere, although with some complexities. Thickened lithosphere beneath the ridge supports lateral conductive cooling beneath slow-spreading centers. Undulations in lithospheric thickness and slow asthenospheric velocities are consistent with small scale convection and/or partial melt. Lithospheric anisotropy can be explained by vertical flow and a contribution from either fluid or mineral filled cracks organized melt beneath the ridge and plate motion induced strain off axis. Deep azimuthal anisotropy is suggestive of upwelling beneath the ridge and three-dimensional flow possibly caused by small scale convection off-axis.},
	keywords = {asthenosphere, azimuthal anisotropy, Lithosphere, Mid-Atlantic Ridge, shear wave velocity},
	issn = {1525-2027},
	doi = {10.1029/2020GC009495},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2020GC009495},
	author = {Saikia, Utpal and Rychert, Catherine and Harmon, Nicholas and Kendall, J. M.}
}
@article {harmon_evolution_2020,
	title = {Evolution of the Oceanic Lithosphere in the Equatorial Atlantic From Rayleigh Wave Tomography, Evidence for Small-Scale Convection From the PI-LAB Experiment},
	journal = {Geochemistry, Geophysics, Geosystems},
	volume = {21},
	number = {9},
	year = {2020},
	note = {_eprint: https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2020GC009174},
	month = {08/2020},
	pages = {e2020GC009174},
	abstract = {The oceanic lithosphere is a primary component of the plate tectonic system, yet its evolution and its asthenospheric interaction have rarely been quantified by in situ imaging at slow spreading systems. We use Rayleigh wave tomography from noise and teleseismic surface waves to image the shear wave velocity structure of the oceanic lithosphere-asthenosphere system from 0 to 80 My at the equatorial Mid-Atlantic Ridge using data from the Passive Imaging of the Lithosphere-Asthenosphere Boundary (PI-LAB) experiment. We observe fast lithosphere (VSV > 4.4 km/s) that thickens from 20{\textendash}30 km near the ridge axis to 70 km at seafloor >60 My. We observe several punctuated slow velocity anomalies (VSV < 4.1 km/s) in the asthenosphere between 50 and 150 km depth, not necessarily focused beneath the ridge axis. Some of the slow velocity regions are located within 100 km of the ridge axis, but other slow velocity regions are observed at distances > 400 km from the ridge. We observe a high velocity lithospheric downwelling drip beneath 30 My seafloor that extends to 80{\textendash}130 km depth. The asthenospheric slow velocities likely require partial melt. Although melt is present off axis, the lack of off-axis volcanism suggests the lithosphere acts as a permeability boundary for deeper melts. The punctuated and off-axis character of the asthenospheric anomalies and lithospheric drip suggests small-scale convection is active at a range of seafloor ages. Small-scale convection and/or more complex mantle flow may be aided by the presence of large offset fracture zones and/or the presence of melt and its associated low-viscosities and enhanced buoyancies.},
	keywords = {asthenosphere, Atlantic Ocean, oceanic lithosphere, PI-LAB, shear velocity, surface wave tomography},
	issn = {1525-2027},
	doi = {10.1029/2020GC009174},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2020GC009174},
	author = {Harmon, Nicholas and Rychert, Catherine A. and Kendall, J. Michael and Agius, Matthew and Bogiatzis, Petros and Tharimena, Saikiran}
}
@article {shintaku_pn_2014,
	title = {Pn anisotropy in Mesozoic western Pacific lithosphere},
	journal = {Journal of Geophysical Research: Solid Earth},
	volume = {119},
	number = {4},
	year = {2014},
	note = {_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/2013JB010534},
	pages = {3050{\textendash}3063},
	abstract = {Pn is the high-frequency, scattered P phase guided for great distances within the old oceanic lithosphere. Two arrays of ocean bottom seismometers were deployed on old (150{\textendash}160 Ma) seafloor in the northwestern Pacific south of Shatsky Rise for the Pacific Lithosphere Anisotropy and Thickness Experiment. We use Pn phases from 403 earthquakes during the 1 year of deployment to measure apparent velocities across the arrays. Each array was deployed on a separate limb of a magnetic bight, formed near a fast-spreading, ridge-ridge-ridge triple junction. Using high-frequency waves (5{\textendash}10 Hz), we look at variations of Pn velocities as a function of azimuth. In the western array, we find Pn anisotropy with velocities ranging from 8.7 km/s in the back azimuth (θ) direction of 310{\textdegree} to 7.7 km/s at 350{\textdegree}. In the eastern array, the velocity ranges from 8.5 km/s in back azimuth direction of 210{\textdegree} to 7.7 km/s at 260{\textdegree} and 310{\textdegree}. We observe rapid velocity changes with azimuth in the both arrays requiring sinusoidal variations of roughly equal amplitude as a function of both 2θ and 4θ, which is not expected for the orthorhombic symmetry of olivine or orthopyroxene. The fastest directions on the two limbs are roughly orthogonal to each other suggesting the dominance of fossil anisotropy, but the fast directions of the 2θ components are skewed counterclockwise from the spreading directions. We speculate that the rapid azimuthal variations may be caused by vertical stratification with changing anisotropy with depth in the oceanic lithosphere.},
	keywords = {anisotropy, asthenosphere, mantle, oceanic lithosphere, Pn waves, western Pacific},
	issn = {2169-9356},
	doi = {10.1002/2013JB010534},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/2013JB010534},
	author = {Shintaku, Natsumi and Forsyth, Donald W. and Hajewski, Christina J. and Weeraratne, Dayanthie S.}
}
